1. Field of Invention
The present invention relates to a system for backlight detection and a method therefor, and more particularly to a system and a method for backlight detection using the brightness values of the subareas in a focus area.
2. Related Art
When an object to be shot is placed between a light source and a camera, a circumstance that a background brightness is much higher than the object to be shot occurs, which is called backlight. The background usually occupies the area larger than the object in an image. Therefore, in the backlight, if the auto-exposure function of the camera is selected, the camera exposes the image according to the light condition of the background, which results in an insufficient exposure of the object to be shot and further causes the shooting failure. In order to avoid the shooting failure when using the auto exposure function, generally the objects are shot while avoiding the backlight. However, there are some methods to avoid the shooting failure in the backlight condition. For example, if the object to be shot is not far away from the camera, a flash light can be turned on to enhance the brightness of the object.
With the progress of science and technology, at present, a technology has been developed to automatically detect whether an object to be shot is in the backlight condition. The common methods usually divide an image into a plurality of areas. For example, the whole image is uniformly divided or divided with a specific shape (for example, the center is a circle and the rest is divided into several parts). After division, different parts are further allocated with different weights. Subsequently, whether the object is backlight condition is determined based on a combination of the information of the parts and other data, such as the overall brightness value of the image (the backlight may occur when the overall brightness value exceeds a specific value) and the scene contrast (the larger the brightness contrast of the object and the background is, the more possible the backlight is).
According to the prior arts, usually, after a focus area is cut from the whole image, information about the contrast and brightness etc. between the focus area and the whole image is calculated. However, in actual environment, it is quite possible that the focus area contains a background with high brightness and an object with low brightness, such that the calculated contrast between the focus area and the whole image cannot reflect the real backlight condition correctly and the success ratio of the determination is thus reduced. In addition, the method of always cutting the focus area is not suitable for all scenes, for example, when the object to be shot slightly offsets or is placed at the border of the darkness and brightness, the determination may be incorrect.